Method of eliminating contaminating metals and metalloids from ores



exited Apr. 30, 1935 ED STATES METHOD or ELiMINA'rnIc coN'rA'r- ING METALS ivm'rnrllorns raoiu' ORES Augustin Leon .lean Qucneau, New York, N. W.

No Bra 1 g. Application January 20, 1928,

Serial No. 248,270

10 Claims.

The various uses of zinc in its various industrial forms or compounds: metal, as slab zinc or rolled products, pigments, asoxides, lithopones, and so forth, often call for a very high degree of purity,

my i. e., freedom from any contaminating metals or metalloids. Further, these pure products command higher prices. The usual metals contaminating slab or rolled zinc are lead, cadmium and iron. The natural ores, crude or concentrates, My often carry other metals and metalloids: sulphur, copper, arsenic, antimony, gold, silver, and so forth. To obtain the metal zinc from its sulphide ores, it is necessary to roast it, thus removing the sulphur as well as arsenic and antimony if present, the sulphide ore being transformed into the oxide. The elimination of sulphur is far from being total in the roasting practice and it has of late become the practice to complete the roasting by a sintering or blast roasting operation. The pre-roasted ore is commonly treated on Dwight-Lloyd sintering machines, the necessary fuel for the operation being supplied either by the sulphur, left in the pre-roasted ore or, if this residual sulphur is too low by a small percentage of carbonaceous fuel, together with 12 to 16 percent water. With the 01d roasting practice the so-called dead roasted ore would carry always over 1 percent of sulphur with pure ore, for example, practically free from lead and alkaline earths, and often 3 or 4 percent of sulphur with impure ores. When the roast has been completed on the sintering machine, whether the ore is pure or impure, the total sulphur is easily brought down to one-half percent or thereabout.-

35 The sintered ore is further more amenable to the subsequent retorting operation.

It ores carry lead, cadmium, silver, gold, copper, and so forth, it is not practical to free them by pyrometallurgy. from these subsidiary metals. The roasted and sintered ore sent to the retorting furnaces will carry these same contaminating metals with perhaps a small reduction in amount in the case of lead, cadmium and silver due to small volatilization losses. If pure metal, slab zinc, has to be produced from these impure roasted, or roasted and sintered, ore either by pyrometallurgy or electrolysis, the only known and applied methods of purification at this date, are wholly by hydrometallurgy. These methods are tedious, slow andcostly and not altogether dependable for a total elimination of these impurities.

The present invention aims to effect the total or substantially total elimination of contaminating metals and metalloids occurring in ores containing zinc, lead, silver, gold, copper and tin by subjecting the pre-roasted and oxidized ore to a so-called blast roasting operation in which operation the blast roast is conducted at relatively high temperatures for short periods of 5 time and the oxidized ore is subjected during this time interval to a chloridizing action whereby all of the metal and metalloid constituents contained therein except the zinc oxide content thereof is eliminated by volatilization. For the purpose of illustration, the method will be described with particularity as applied to zinc ores but it is to be understood that the method is in no way limited to use in connection with such ores.

An important feature of my invention resides in the step of mixing the ores to be treated with a chloridizing agent and igniting and passing a blast of air through the mixture. The improved method is applicable to either sulphides or oxides or mixtures of them and can be carried on by the use of known types of blast masters and sintering machines now in general use. For example, in the treatment of zinc ores, I may use the Dwight-Lloyd or other sintering apparatus. In the treatment of zinc, I follow quite closely the sequence of operations now followed in the industry. That is to say, the ore is preroasted, sintered and finally treated in retorts. But in my method I substitute what I call a chloridizing blast step for the usual sintering step. This chloridizing and sintering consists in mixing with a pre-roasted ore containing say 8 to 10 percent sulphur and 12 to 16 percent water or pre-roasted ore with 2 to 4 percent sulphur with two or three percent carbon and the same amount of water, the required amount of a cheap and commonly found chloride; such as, ordinary salt, N aCl, or calcium chloride, CaCl2, magnesium chloride, MgCl2, or mixtures of any or all of these and either in the solid form or in any convenient solution, sea. water, natural brines, and so forth. Further, these salts or solutions need not be pure. They may contain other chlorides and sulphates or mixtures of these. n

The chloridizing blast which I use is especially destructive to any and all sulphates. These are broken up and the sulphur is volatilized.

The amount of the chlorides required to eliminate the metals and metalloids is calculated to supply the required chlorine to satisfy these metals and metalloids in the form of their chlov rides, and with a small excess so that there is'at all times present an atmosphere rich in chlorine or its compounds in the bed of the sintering machine. The exact and specific amount cannot be laid down in general terms, or mathematical rule. It will vary with the many varied ores, in their many mineralogical compositions and physical characteristics. Usually, preliminary test runs have to be made to determine the exact economical proportion of chlorides required for any specific case. I may also use, but in smaller proportion, bromides or iodides or mixtures of all of these.

To enable those skilled in the art to fully comprehend the invention, I give below a specific example of an actual reduction to practice.

A pre-roasted Joplin zinc concentrate, assaying as sent to the Donora, Pennsylvania, sintering plant, zinc 61.75 percent; total sulphur 4.35 percent of which .75 percent occurred in the form of soluble sulphate; lead .625 percent and cadmium .170 percent. This pre-roasted ore was mixed with ground coke, the mixture carrying 1.86 percent carbon, and with 58 lbs. per ton of common salt. Water was added previous to the mixtures entering the pugmill so that the final mixture carried 11.80 percent water.

The mixture passed to the sintering machine, then under the ignition burners. The resulting sinter, which was fairly hard and of excellent physical characteristics, had the following percentage analysis: water 1.00, zinc 67.80, sulphur in any form .000, lead .000, cadmium .020.

With such sinter a high grade slab zinc can be obtained in the usual retorting practice along lines well known to those skilled in the art. From this high grade slab zinc, by the French Process, high grade zinc white can also be secured by burning the metal and collecting the oxide. Such an oxide will be suitable for any and all of the uses calling for pure zinc white, pharmaceutical, pigments, rubber trade, and so forth.

In the same manner this highly purified sinter can be used for the manufacture of electrolytic zinc, either by the chloride or the sulphate methods. In the case of the sulphate, the chlorides in any and all forms being highly detrimental, the sinter would receive a thorough washing until it has been freed from all but minute traces of chlorine. This would obviate the costly and tedious methods heretofore used in the electrolytic zinc industry to free the crude sulphate solutions now obtained by leaching the roasted zinc ore with sulphuric acid. These solutions require elaborate treatment for the removal of arsenic, antimony, iron, copper, lead, cadmium, and so forth. By my chloridizing blast roast treatment herein described, the arsenic, antimony, lead, cadmium and sulphur may be eliminated in toto. The two impurities that are the most difficult in electrolytic practice to remove are lead and cadmium, but especially the latter.

In the present pyrometallurgy, the retorting method for the recovery of lead and precious metals is quite imperfect and costly, involving many steps and, of course, many losses incidental to these repeated steps. The metals remaining in the sinter, or roasted ore if the sintering process is not used, pass to the retorting plant and remain with the retort residues, from which they are recuperated either by wet concentration and by smelting of the concentrates or by direct smelting. It may be stated that in the prior practice at most not over 65 percent of the lead and silver contents contained in the original concentrates received in the zinc retorting plant are finally secured in a commercial form,-lead bullion.

The use of the present invention simplifies the recovery and especially increases the quantity recovered. By my chloridizing blast, the lead, cadmium, silver and gold are removed in the form of chlorides and fume, and collected'in suitable apparatus, such as a Cottrell electric precipitator. The collected chloride and fume can be treated by any of the methods well known to those skilled in the art.

The above described method is available not only for the production of high grade slab zinc from zinc ores containing only small amounts of lead, 1 to 2 percent, and cadmium percent but alsofrom ores carrying substantial amounts of lead and precious metals. It may be necessary to retreat the sinter obtained in a chloridizing blast roast to a second such operation when the original ores contain high amounts of lead and other impurities. The sintering temperature employed is preferably greater than 1000 C. In the case of zinc, the mixture will be .sintered at a temperature between 1000 C. and 1500 C. By passing a. blast of air through the mixture, it will be apparent that the volatile chlorides from the mixture are all carried away from the charge as rapidly as they are formed. These volatile products are in a highly concentrated form; hence the metallic values can be readily recovered. An important feature of my process is that such metallic values in a highly concentrated form have been completely divorced from the earthy gan'gue or dross.

The chloridizing roasting process operated either with a chlorine bearing material alone or in combination with carbonaceous materials together with the ore, is available to the metallurgy of other ores besides the ores which have for their main value the zinc contents. The process is applicable to metallurgy of any and all metals whenever it is the aim to extract the metal contents by transforming them into chlorides. The process is applicable, for example, to the treatment of silver ores with or without lead and zinc values; likewise, to gold ores with or without allied base metals. In the same manner it is applicable to the metallurgy of copper ores and of tin ores. It is especially applicable in this instance where the tin ore is contaminated with other metals or metalloids. In a Word, we have here a general process applicable to all ore treatment from which the metal contents would be extracted by the action of chlorine and hydrochloric acid at a high temperature.

I thus provide a powerful and low cost method with large tonnages per hour and per machine, which is not the case with any of the previously known methods of chloridizing. Its excellence proceeds from the conditions prevailing in the bed of the sintering machine. We have intimate mixture between the ore and the reagent due to the mechanical mixing in the pugmill and also to the relatively large percentage of water incorporated in the charge, 12 to 16%. The ore and chloridizing mixture is first subjected to the ignition burner and as it travels over the vacuum boxes of the sintering apparatus, the combustion proceeds with great rapidity and each and every particle of ore of the bed is subjected to an intense temperature often reaching from 1000 C. to 1500 C. This chloridizing agent under these conditions vigorously reacts with the metals and metalloids as described and the volatile chlorides and fume are immediately expelled for further treatment.

The term ore used in the claims is intended to include ores, concentrates and other metallurgical products.

Various modifications of the invention may be made by those skilled in the art without departing from the invention as defined in the following claims.

What I claim is:

1. In the recovery of zinc from its ores, the method of eliminating associated metal and metalloid impurities therefrom which comprises oxidizing the metal values of the ore adding carbon, a chloridizing agent and water thereto and then simultaneously chloridizing and blast sintering the oxidized ore at elevated temperature in excess of about 1000 Czsufiicient to chloridize and to vaporize substantially all of the associated metal and metalloid impurities.

2. In the recovery of zinc from its ores, the method of eliminating associated metal and metalloid impurities therefrom which comprises oxidizing the metal values of the ore adding carbon, a chloridizing agent and water thereto and then simultaneously chloridizing and blast sintering the oxidized ore at temperatures between 1000 C. and 1500 C. sufiicient to chloridize and vaporize substantially all the associated metal and metalloid impurities.

3. The method of chloridizing and blast sintering oxidized zinc sulfide ores to eliminate associated metal and metalloid impurities therefrom which comprises admixing the ore with sodium,

chloride, water and carbonaceous material and blast sintering the same, the proportion of carbonaceous material added being at leastsufilcient to incandesce the sintering material to temperatures in excess of about 1000 C. sufllcient to vaporize substantially all of the associated metal and metalloid impurities.

compounds, which comprises admixing there-- with a chloridizing agent, a proportion of carbon and water and heat treating the admixture in an oxidizing blast to temperatures in excess of 1000 C. to chloridize and to vaporize substantially all the associated metal and metalloid impurities.

6. The method of treating oxidized zinc ores containing from 8 to 10% sulfur a proportion of which sulfur is comprised of water soluble sulfate compounds, and a proportion associated chloridizable metal impurities which comprises admixing therewith carbon, water and sodium chloride in excess of that amount required to combine with the said associated impurities and heat treating the admixture in an oxidizing blast to temperatures above about 1000" C. to chloridize and vaporize substantially all metal and metalloid values in the ore except zinc.

7. The method of treating zinc sulfide ores comprising oxidizing said ore, admixing therewith a chloridizing agent, carbon and water, heat treating the admixture in an oxidizing blast to temperatures in excess of 1000 C. to chloridize and to vaporize therefrom substantially all metal and metalloid values except the zinc and thereafter admixing the residue with carbon and retorting to recover the zinc content thereof.

8. The method of treating zinc sulfide ores comprising oxidizing said ore, admixing therewith a chloridizing agent, carbon and water, and

sintering the admixture in an oxidizing blast at temperatures in excess of 1000 C. to chloridize and to vaporize therefrom substantially all metal and metalloid values except the zinc and thereafter admixing the residue with carbon and retorting to recover the zinc content thereof.

9. The method of treating oxidized zinc ores comprised in part of associated chloridizable metal impurities and sulfur which comprisesadmixing a chloridizing agent, carbon and water therewith and heat treating the admixture in an oxidizing blast to temperatures in excess of the volatilization temperature of cadmium chloride to chloridize and to vaporize substantially all the associated metal and metalloid impurities.

10. The method of treating zinc sulfide ores comprising oxidizing said ore, admixing therewith achloridizing agent, carbon and water and sintering the admixture in an oxidizing blast at temperatures in excess of the volatilization temperature of cadmium chloride to chloridize and to vaporize therefrom substantially all metal and metalloid values except the zinc and thereafter admixing the residue with carbon and retorting to recover the zinc content thereof.

AUGUSTIN LEON JEAN QUENEAU. 

